Polycarbonate (PC) resin is a thermoplastic resin that has excellent impact resistance and is rigid and light. Polycarbonate resin it is often used in a form of an alloy with other polymers due to its poor fluidity.
For example, when an acrylonitrile-butadiene-styrene (ABS) resin is blended with polycarbonate, the resulting resin composition maintains the impact resistance of the polycarbonate while exhibits improved fluidity, and it may be provided with a relatively low cost, as well. Therefore, the PC/ABS alloy is commonly used in an interior/exterior part material for a vehicle or a housing material for electronic devices, office machines, and the like.
When a PC/ABS alloy is used, however, to manufacture an injection-molded article using a mold with two or more gates, a phase-separation phenomenon noticeably occurs at a flow end where compositions inflowing from each gate meets each other. This may cause a weld line as the alloy has inherently two phases originating from polycarbonate (PC) and styrene-acrylonitrile copolymer (SAN), respectively, in the compositions. Such a weld line is vulnerable to impact. Thus if an article having such a weld line is subject to an impact, it may be easily broken without showing whitening phenomenon.
In order to address the aforementioned problems, there have been made many attempts to increase viscosity of the SAN so as to decrease the viscosity difference with the PC or to use an acrylate-based compatibilizer to inhibit the weld line formation. However, such measures may result in a higher viscosity of the resulting resin composition, which in turn can adversely affect the fluidity thereof. In addition, an excessive amount of the compatibilizer used in the composition may significantly deteriorate molding properties. When the resin composition having unsatisfactory fluidity or poor molding properties is subjected to an injection molding process to produce a large molded article such as parts for vehicles or an articles having a complicated shape, the resulting product can have fatal defects.